TypeError: ObjectId("") is not JSON serializable

How to Fix the "TypeError: ObjectId('') is not JSON serializable" Error in MongoDB with Python

Are you encountering the frustrating "TypeError: ObjectId('') is not JSON serializable" error while working with MongoDB and Python? Don't worry, you're not alone! This common error occurs when you try to serialize an object containing an ObjectId from MongoDB into JSON format.

In this blog post, we'll explore the underlying issue causing this error and provide you with easy-to-implement solutions. So, let's dive in!

Understanding the Error

Before we proceed any further, let's understand what is happening when the "TypeError: ObjectId('') is not JSON serializable" error occurs.

When you query MongoDB and receive a response, it's returned as a Python dictionary. This response may contain special MongoDB data types, such as ObjectId. The issue arises when you try to convert this dictionary into JSON format using the json.dumps() function.

As you may already know, json.dumps() is a Python method used to convert a Python object into a JSON-formatted string. However, it cannot directly handle MongoDB-specific data types like ObjectId, resulting in the "TypeError" we're discussing.

Solution 1: Using a Custom JSON Encoder

One way to tackle this issue is by using a custom JSON Encoder. Python's json module allows you to define a custom encoder class that can handle the serialization of special data types. Here's an example of how you can implement it:

import json
from bson import ObjectId

class JSONEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, ObjectId):
            return str(o)
        return super().default(o)

# Usage
data = {'result': [{'_id': ObjectId('51948e86c25f4b1d1c0d303c'), 'api_calls_with_key': 4, 'api_calls_per_day': 0.375, 'api_calls_total': 6, 'api_calls_without_key': 2}], 'ok': 1.0}
json_data = json.dumps(data, cls=JSONEncoder)

Here, we define a custom JSONEncoder class that extends the json.JSONEncoder class. We override the default() method to handle ObjectId instances, converting them into strings using the str() function. This ensures that the serialization process proceeds smoothly.

Solution 2: Converting ObjectIds Manually

Another approach is to manually convert the ObjectId instances into strings before serializing the Python dictionary into JSON. You can achieve this by iterating through the dictionary and explicitly converting any ObjectId you encounter.

Here's an example of how you can do this:

from bson import ObjectId
import json

data = {'result': [{'_id': ObjectId('51948e86c25f4b1d1c0d303c'), 'api_calls_with_key': 4, 'api_calls_per_day': 0.375, 'api_calls_total': 6, 'api_calls_without_key': 2}], 'ok': 1.0}

def convert_to_json(data):
    if isinstance(data, dict):
        for key, value in data.items():
            if isinstance(value, ObjectId):
                data[key] = str(value)
            elif isinstance(value, dict):
                convert_to_json(value)
            elif isinstance(value, list):
                for item in value:
                    convert_to_json(item)

convert_to_json(data)
json_data = json.dumps(data)

In this approach, we define a recursive function, convert_to_json(), that iterates through the dictionary and checks each value. If a value is an ObjectId, it is converted into a string using str(). This ensures that the dictionary is ready for JSON serialization.

Conclusion

Dealing with the "TypeError: ObjectId('') is not JSON serializable" error can be frustrating, but now you have two proven solutions at your disposal. Whether you choose to implement a custom JSON Encoder or manually convert ObjectIds into strings, you're set for success.

Now, go ahead and try out these solutions! Feel free to let us know which one worked best for you in the comments below. And if you have any other questions or solutions to share, we'd love to hear from you! Happy coding! 😄👍